1. Field of The Invention
The subject invention relates to the display of color video and data graphic signals, and more particularly, to displaying color video and data graphic signals on a linear display.
All video and data graphic sources assume that the information will be displayed on a CRT-like device, i.e., a display device with a non-linear luminance output/electrical input function. The assumed function is the so-called gamma function, where V.sub.OUT =V.sub.IN.sup..gamma., where .gamma.=2.2-2.8. However, various flat displays, including plasma display panels (PDP's), have a linear response, i.e., .gamma.=1.0. If this discrepancy is not corrected, the displayed picture has a pale appearance with little color saturation.
2. Description of The Related Art
Typically, digital video signal processing is carried out using 8 bits. As shown in FIG. 1, after analog-to-digital conversion in A/D converter 10, a gamma look-up table 12 can be used to interface between the 8-bit processing and an 8-bit PDP 14. Here, the look-up table 12 uses a list of 256 8-bit values for each color, each of these values being corrected with respect to gamma. The most common way of realizing the look-up table 12 is by using a (P)ROM or a RAM.
In the case of a 10-bit PDP, U.S. patent application Ser. No. 09/191,842, filed Nov. 13, 1998, assigned to the Assignee of this application, discloses a circuit for converting an 8-bit input video signal into a 10-bit gamma corrected output video signal for application to a PDP.
FIG. 2 shows a graph of a gamma curve (solid line), where gamma (.gamma.)=2.2. As can be seen, the curve is very flat at the beginning, at low grey levels. This means that a large number of input codes are mapped onto a few output codes resulting in a loss in resolution.
Alternatively, it is known to use linear approximation to correct for gamma in a video signal. As shown in FIG. 3, the output from the A/D converter 10 is applied to a linear approximation circuit 16 which then applies the gamma corrected video signal to the linear display 14. Samsung Electronics markets a color decoder containing a programmable gamma correction unit KS0127 which allows a user to apply many different types of corrections. Depending on the type of correction needed, only a limited number of values are stored in the unit, and the unit uses linear interpolation to generate the in between values. FIG. 2 also shows a graph of a linear approximation curve (dotted line) in which 4 linear segments are used. However, the results have not proven to be acceptable, in that errors occur where the linear approximation curve deviates from the (ideal) gamma curve.